Radio receiving system



W. R. KOCH RADIO RECEIVING SYSTEM June 1, 1937.

2 Sheefl-Sheet 1 yFiled May 27, 1929 ATTORNEY `,une l, 1937. w, R KQCH 2,082,767

RADIO RECEIVING SYSTEM Filed May 27,` 1929 2 sheets-sheet 2 wAlTNEssEs: |NvENToR Patented June 1, 1937 UETE STATES RADIO RECEIVING SYSTEM Winfield R. Koch, Wilkinsburg, Pa., assigner Ato Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application May 27, 1929, Serial No. 366,357

9 Claims.

My invention relates to radio systems and particularly receiving systems of the type wherein a plurality of tuning reactors are connected together for simultaneous actuation.

More especially, my invention is concerned with radio receiving systems `of the type known as superheterodynes, wherein a local oscillator is employed for changing the frequency of an incoming carrier wave to either a lower or a higher frequency before amplification and de modulation.

Superheterodyne systems, as at present constructed, have many advantages over systems of the straight amplifier-detector type but trouble has heretofore been experienced in preventing them from responding to undesired frequencies which differ from the frequency of the oscillator by an amount equal to one-half of the difference in frequency between the desired frequency and the said undesired frequencies. Such undesired frequencies are known as image frequencies. It has also been found diflicult to so arrange the various circuitsthat the rotors of all of the tuning eondensers may always be maintained at ground potential, insofar as radio frequency is concerned.

Superheterodyne receiving systems have also, by reason of their extreme sharpness of tuning, been somewhat unsatisfactory, insofar as vthe quality of music reproduction is concerned.

It is, accordingly, an object of my invention tol provide a radio receiving set of the superheterodyne type wherein all of the necessary tuning condensers may be maintained at ground po- 3.. tential, insofar as radio frequencies are concerned.

Another object of my invention is to provide a radio receiving set of the type described wherein the selectivity is improved without sacrifice of 4U tonal quality.

Another object of my invention is to provide a radio receiving set of the type described wherein a common source of plate potential may be utilized without causing the generation of unde- 45 sirable oscillations.

Another object of my invention is to provlde a radio receiving system that shall be relatively insensitive to extraneous and interfering disturbances.

Another object of my invention is to provide a radio receiving `system wherein the gridbias ing potentials for all of the necessary thermionic tubes may be derived from a common source of plate potential in such manner as to preclude the veneration of undesired oscillations.

Another object-of my invention is to provide, 1n a receiving system of the type describedfa plurality of independent means for volume-control. v Y

Another object of my invention is to provide a radio receiving system that shall comprise devices for simulating the action of a `band-pass lter. f i y I Another object ofmy invention is to provide a radio receiving system, the tuning of which -isunaffected by changes in `the `energy-receptor or antenna to which it is connected.

A still further and more specific object of m invention` is to provide a-radio receiving system that shall be equallywell applicable to the reception of telephone signals or continuous-wave.-

telegraphic signals.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. Inasmuch as the invention itself, however, comprises numerous elements and sub-elements, all combining to permit the attainment of the yaforementioned robjects and other objects hereinafter referred to,

it will best be understood from the followingrde-l scription of a specific embodiment, .when read in connection with the accompanyinggdrawings.

Fig. 1 of the drawings isa diagrammatic View of a complete radioreceiving system .ofY the superheterodyne type comprising preferred embodiments of my invention.

Fig. 2 illustrates a modification of the radio frequency portion of the circuit of Fig. 1.

A receiving system illustrated in Fig. 1 Vcom-f prises a coupling tube I, a rst radio frequency amplifying tube 2, a second radio-frequency am@V plifying tube 3, a first detector tube ,4,to` which is coupled an oscillation generator 5, a rst Each of the tubes in the receiving system is of the equipotential-cathcde type, comprising anv anode 2G, a control grid 2 I, a thermionic cathode 22, and a cathode heater 23. The choice of tubes of this particular type, in connection with the circuits later to be described, is an intentional part of my invention.

The radio receiving system is supplied with cathode-heating current, grid-biasing potentials and plate potentials from a rectifier 24 which is arranged according to the description on page 141 5 of the publication by Van der Bijl, "Thermionic Vacuum Tubes, and needs no specific description. The use of a plurality of equi-potential cathode tubes 25 and 26 in the rectifier, however, is a part of my inventive thought, inasmuch as it permits the energizing of all of the cathodes in the radio receiving set proper from the same source that is utilized to energize the said rectifier tubes.

The rectifier is provided with an output resistor 21 across which is developedv approximately twice the potential delivered by the secondary winding 28 of the power transformer 30, in the manner explained in the aforesaid Van der Bijl publication.

A plurality of conductors 3|, 32, 33, 34, 35 and 36 extend from points on the output resistor that are maintained at +200, 90, +45, zero, 4.5, and -9 volts, respectively. These conductors will be later referred to as bus-wires in describing the manner in which the various grid, plate, and cathode potentials are supplied to the receiving system.

Before attempting to explain the specific manner in which the various objects of my invention are attained, it is considered advisable at this point, to briefly describe the manner in which the system operates in the reception of continuous-wave signals. For purposes of explanation, it is assumed that it is desired to receive an incoming signal of the continuous wave type having a carrier frequency of the order of 500 kc.

The carrier frequency, together with other incoming frequencies and disturbances, is impressed across a resistor 40, one end of which is connected to the grid of the coupling tube and the other end of which is connected to the cathode of the tube through a condenser 4I, an inductor 50 and a condenser 5I. The purpose of the circuit 50-5I will be hereinafter described in detail.

The amplied signal then traverses the rst and second RF amplifying tubes 2 and 3 the input circuits of which are tuned to the frequency of the incoming signal, and is impressed upon the input circuit of the first detector tube 4. The

first RF oscillator 5 is so adjusted if the incoming signal is at a frequency of 500 kc., as to generate oscillations at a materially higher frequency, 1000 kc. signals being a good value to choose in the specic example given. Beatfrequencies of 500 kc. and 1500 kc. will, accordingly, exist in the output circuit of the rst detector tube I, and either of these frequencies may be chosen for further amplification. In

50 order that the selectivity of the system may be improved, I find it preferable to choose the higher frequency, namely, 1500 kc. and the input circuit of the highest intermediate frequency tube E is accordingly tuned thereto.

'I'he output of the higher intermediate frequency tube 6 is impressed on the input circuit of the second detector tube 'I wherein, by reason of the action of the second high-frequency 70 oscillator 8, it is altered to either a higher or to a lower second intermediate frequency, and is thereafter amplified by the second intermediatefrequency amplifier tube I I.

If the incoming signal is of the continuous- 75 wave type a beat-frequency oscillator may be utilized to reduce the signals to an audible note for further amplification.

The second intermediate frequency is demodulated in the third detector tube I2, and the resulting audio-frequencies are next impressed upon the rst audio-frequency amplifier tube I3, and, thereafter, upon the second audio-frequency or power-amplifier tube I4.

By reason of the successive heterodyning of the incoming signal by the first and second. high-frequency oscillators, the desired signal may be Widely separated from interfering signals before amplification in the second intermediate amplifier. This feature is of particular value, under present conditions, since signals from many stations, which would otherwise interfere, and which lie Within the range of receiving sets of the usual superheterodyne type, are thus prevented from being heard.

In addition to the general arrangement of the circuits thus far described, my invention further consists in the specific circuit details of the various stages, which details, in their entirety, mutually contribute toward sensitivity, selectivity and ease of operation. These details Will now be:

taken up in their proper order, and an effort Will be made to point out the novel features of each.

It will be noted that an inductor 50 and a Variable condenser 5I are included in the cathode circuit of the coupling tube I, a radiofrequency choke-coil 52 being connected in shunt to the variable condenser. The inductor and the condenser constitute a tunable circuit that may be adjusted to the frequency of the desired incoming signal, to a slightly higher frequency or to a slightly lower frequency. When the circuit is adjusted to the frequency of the desired signal, the coupling tube will amplify the said signal to the exclusion of signals at adjacent frequencies, irrespective of the fact that the input circuit of the tube is aperiodic.

As shown in Fig. 2 of the drawings, one or more radio-frequency amplifying stages |23 and I24 for example, may be interposed between the coupling tube I and the rst radio-frequency tube 2, each of the stages preferably comprising an equi-potential cathode tube, the cathode circuits of which may include reactors |25 and I26 similar to the reactors 50 and 5I in the cathode circuit of the coupling tube. By tuning one of the said stages to a frequency somewhat lower than the desired frequency and by tuning another of the stages to a frequency higher than the desired frequency, a band-pass filter effect may be secured without resorting to expensive band-pass filters. In fact, the shape of the response curve. of the receiving system may so be adjusted as to have any desired contour.

It is often desirable, in the event that the receiving system is used at a point closely adjacent to a higher-power transmitter, to interpose a wave trap in the input circuit thereof. It is much better, however, to incorporate means equivalent to a wave trap directly in the receiving system itself. For that reason, I have included a parallel resonant circuit, constituted by an inductor and a tuning condenser 6I, in the cathode circuit of the first radio-frequency tube 2. When this circuit is tuned to a strong interfering signal, it prevents the rst radio-frequency stage from amplifying the said signal and, although the interfering signal may be impressed upon the input circuit of the said radio-frequency stage, it will not be amplied and appear in the output circuit thereof. The circuit Sil- 6| also has the important function of reducing image-frequency response, when properly tuned.

It often happens, in the operation ofV sensitive tuned radio-frequency amplifiers, that parasitic oscillations at ultra-high` frequencies, orat high frequencies lying within thetunng range, are

developed. In order that such oscillations may be minimized', I have included a variable reactor 62 in the cathode circuit of the second radiofrequency amplifying tube. This reactor, Awhen properly adjusted, tends to stabilize the system and to prevent oscillations at high frequencies.

As previously pointed out, it is highly desirable that the rotors of all the tuning condensers shall be maintained at ground potential, insofar as radio frequency is concerned. It is also desirable that the various oscillation generators and the amplifying tubes shall be supplied with plate potential from the same source. In addition, I have established the fact that an oscillatorof the socalled Hartley type is, perhaps, the best to use in a superheterodyne receiver. These desirable features cannot be satisfactorily attained if thermionic tubes of the usual filament type are employed, since it is impossible to maintain, the filaments thereof at varying potentials with respect to each other, inasmuch as they must all be supplied Wlth power from the same source. By choosing equi-potential cathode tubes, however, I am enabled to maintain any desired potential differences between the grids and cathodes thereof, between the anodes and grids thereof, between the anodes and cathodes thereof and between the several cathodes.

Itl will be noted, from an inspection of the drawings, that a coupling coil 63, Yfor the first oscillator 5, is serially connected between the cathode of the rst detector tube 4 and the buswire 34, which wire is maintained at effective ground potential, insofar as radio frequency is concerned, by reason of the b-y-pass condenser 4I, connected between it and the ground. The rotor of a tuning condenser 64, comprised in the input u circuit of the first detector tube, and the rotor fore, not quite so effective as in systems vof the usual type, but the slight lack of effectiveness is more than compensated for by the advantages accruing from the grounding o f the condenser rotors. v

Inasmuch as thecathode of the oscillator tube has an inappreciable capacity to ground, nodeleterious effects arise from grounding the rotor of the condenser. It should be apparent to those skilled in the art that these results cannot be obtained without complicated circuits, when using detector and oscillator tubes having filamentary cathodes supplied from the same power source. In order that the volume of the signal output from the entire system may be easily controlled, I have included a variable resistor l0 in the cathode circuit of the first high-intermediatefrequency amplifier tube E. Since the entire plate current in the said tube must, of necessity, traverse the resistor,` the, potential, zappled to the plate of the tube obviously is altered with changes in the magnitude of the resistor.

It will also be noted that a connection 'H eX- tends from the midpoint of the inductor constitutingv the input circuit of the said tube to the bus-wire 35 which is maintained at 41/2 volts and that, accordingly, any change in potential between the anode and the cathode of the tube, occasioned by a variation of the resistor 70, is accompanied by a 'change in the potential of the grid with respect to the saidcathode. The volume-control resistor 'l0 therefore, serves to control the amplification in the rst high-intermediate-frequency amplifier both by occasioning variations infthe plate potential appliedrthereto and in the grid potential with respect to the cathode thereof.

The second high-frequency oscillator is coupled to the second detector through an inductor that is included in the cathode circuit of the said tube. The advantage of this type of coupling has been previously mentioned in connection with the rst detector tube.

The beat-frequency oscillator is coupled to the second high-frequency oscillator through an indeenergizing it in the event that the incoming signals are not of the CW type.

It will be seen, from a close inspection of the drawing, that the circuits of the three oscillation generators 5, 8 and l0 differ in details although each of the three circuits is essentially of the Hartley type. The circuits so shown are interchangeable and are given merely to illustrate thev manner in which my invention permits the grounding of the rotors of the tuning condensers associated therewith. The circuits of the first radio-frequency oscillator and the beat-frequency oscillator are perhaps the most satisfactory of the three circuits illustrated.

A volume-control network of alternative type is shown in connection with the second intermediate-frequency amplifier stage. The network comprises a resistor 9B connected in shunt to the -B and +45 volt terminals of the output resistor of the power supply. A connection 9| is made between the cathode of the amplifier tube "and a movable contact device 92 associated with the resistor. 'Ihe potential of the cathode with respect to both the anode and grid of the tube may, accordingly, be varied by moving the contact device toward either thepositive or the negative end of the resistor.

The input circuit of the third detector tube I2 preferably comprises a grid leak il and a grid condenser IIN. Plate potential for the third detector tube is supplied from the +200 volt buswire over a variable resistor |02.

The grid of the first audio-frequency amplifier tube I3 is directly connected to the plate of the third detector tube, and the potential of the said grid is, accordingly, determined by the IR drop along the variable resistor. A connection 103 extends from the cathode of the first audiofrequency amplifier tube to the volt bus wirefand plate potential for the tube Vis supplied from the +200 volt bus-wire. A potential difference of volts, therefore, would normally exist between the grid of the tube I3 and the cathode thereof but, by properly adjusting the no-signal plate current in the third detector tube I2, the potential drop along the variable resistor. may be so determined that the grid of the said tube assumes a sufiiciently negative potential to bias it almost to the cut-off point.

An incoming signal, however, causes a diminution in the plate current of the third detector tube. The IR drop in the variable resistor is, accordingly, lessened to a value which permits the grid of the rst audio-frequency tube to acquire a sufciently less negative potential to permit satisfactory amplification of the fluctuating audio-frequency potentials existing across the variable resistor by reason of the incoming signals.

An ammeter |20 is preferably included in the cathode circuit of the third detector tube |2 as an aid in determining when the signal is properly tuned in, accurate tuning being indicated by minimum current through the ammeter.

A loud speaker |2I, or other signal indicator, is preferably included in the cathode circuit of the second audio-frequency amplifier tube i4, and a resistor |22 is connected in series therewith.

The grid of the amplifier tube I4 is connected to the resistor |22 at that end to which the loud speaker is also connected. The plate Vcurrent flowing in the resistor, accordingly, determin-es the grid potential, and the tube is thus automatically biased to the best operating point.

From a careful consideration of the foregoing description of a superheterodyne receiving system comprising my invention, it will be apparent that, by utilizing tubes of the equi-potential type, I am enabled to provide a receiving system that has many advantages, among which may be mentioned extreme selectivity, sensitivity, simplicity,

`fidelity of reproduction and lessened danger to the operator from high potentials.

Although I have illustrated my invention as particularly applicable to receiving systems of the superheterodyne type, it is equally useful in other receiving systems of the types well known to those skilled in the art. The description of certain specilic circuit details in connection with particular stages of the systems is not to be construed as an admission that the said details are only useful in the said stages. For example, the tuning ammeter |20 might well be included in the cathode circuit of the first detector, or in the cathode circuit of the second detector, with substantially the same results. The several oscillation generators 5, 8 and I8, might all comprise circuit-networks of the same type as the circuit network described in connection with any one of the said generators. In fact, substantially all of the circuit details shown are capable of use in positions vother than those speciiically illustrated.

My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art or by the spirit of the appended claims,

I claim as my invention:

1. In a radio receiving system, an electron discharge device having a grid and a cathode electrode, and an input circuit for said device comprising a resistor, a capacitor, and an inductor serially connected between said grid and cathode electrodes, said capacitor and inductor being series tuned to the frequency of an incoming signal.

2. In a radio receiving system, a plurality of electron discharge devices connected in cascade,

and means for obtaining the effects of a bandpass lter insofar as the amplifying characteristics of said devices are concerned, said means comprising tunable impedances in the cathode leads to certain of said devices, the impedance oii'ered by said tunable impedances being different for any particular adjustment.

3. In a radio receiving system, a source of positive and negative potentials, an electron discharge device of the equipotential cathode type, connections between the anode, the cathode and the grid of said device and said source and a variable resistor included inthe connection between the cathode and said source, said variable resistor serving to simultaneously vary the potential between the anode and the cathode as well as the grid and the cathode of said device for purposes of volume control.

4. In a radio receiving system, an electron discharge device of the equipotential-cathode type, a tuned input circuit for said device connected between the grid thereof and said cathode, an output circuit including a source of potential, said output circuit being connected between the anode of said device and said cathode with the negative end of said source of potential at the cathode end of the circuit, the connection to the cathode being common to both said input and output circuit, and an inductor in said common connection for reducing the amplication of said device at high frequencies.

5. In combination, a plurality of electron discharge devices having indirectly heated cathodes, circuits including inductive couplings for coupling said discharge devices to constitute a radio system, a common source of potential for said discharge devices, manually variable condensers in said circuits for tuning said inductive couplings tov desired frequencies of operation, each of said condensers having fixed and movable elements, and a conductive interconnection between similar elements of said condensers.

6. In combination, an electric discharge device comprising an indirectly heated cathode, a control element and an anode, an input circuit for said device including said control element and said cathode, an output circuit for said device including said anode and said cathode, an oscillation generator comprising an electron discharge device having an indirectly heated cathode, a control electrode and an anode, input and output circuits for said device including said discharge device electrodes, means for coupling said oscillation generator to said iirst electric discharge device and its circuits, tuning condensers in the circuits associated with each of said discharge devices, and a connection between said condensers at effectively ground potential.

'7. In a radio system, an electron discharge device having an independently heated source of electrons, a plate circuit including a source of positive potential, a grid circuit having a portion in common with said plate circuit and means for varying said common portion to directly produce simultaneous eifects in both said plate and grid circuits.

8. In combination, a plurality of electron discharge devices, at least one of said devices having an indirectly heated cathode, circuits including inductive couplings for coupling said discharge devices to constitute a radio System, a common source of potential for said discharge devices, normally variable condensers in said circuits for tuning said inductive couplings to desired frequencies of operation, each of said condensers having fixed and movable elements, and a conductive interconnection between similar elements of said condensers.

9. In combination, an electric discharge device comprising an indirectly heated cathode, a control element and an anode, an input circuit for said device including said control element and said cathode, an output circuit for said device including said anode and said cathode, an'oscillation generator comprising an electron discharge device having a cathode, a vvcontrol electrode and an anode, input and output circuits for said device including said discharge device electrodes, means for coupling said oscillation generator to said rst electric discharge devices and its circuits,compris ing an impedance in the cathode lead of said first device coupled to one of the circuits of said second discharge device, tuning condensers in the circuits associated with each of said discharge devices, and a connection between said condensers at effectively ground potential.

WINFIELD R. KOCH. 

